This invention relates to retroreflective articles having prismatic retroreflective elements.
Many types of retroreflective articles are known, and are made in a variety of ways. One common type of retroreflective article uses transparent microspheres, typically with hemispheric retroreflectors thereon. Examples of this type of retroreflector are disclosed in U.S. Pat. No. 2,407,680 (Palmquist), U.S. Pat. No. 3,190,178 (McKenzie), and U.S. Pat. No. 4,025,159 (McGrath).
Another type of retroreflective article includes prismatic designs incorporating one or more structures commonly known as cube corners. Retroreflective sheeting which employs cube corner type reflective elements is well known. An example of such designs is shown in U.S. Pat. No. 3,684,348 (Rowland).
The manufacture of retroreflective cube corner element arrays is accomplished using molds made by different techniques, including those known as pin bundling and direct machining. Molds manufactured using pin bundling are made by assembling together individual pins which each have an end portion shaped with features of a cube corner retroreflective element. For example, certain pin bundled arrays permit elaborate assembly into various pin structural configurations. U.S. Pat. No. 3,926,402 (Heenan et al) and U.S. Pat. No. 3,632,695 (Howell) are examples of pin bundling.
The direct machining technique, also known generally as ruling, comprises cutting portions of a substrate to create a pattern of grooves which intersect to form cube corner elements. The grooved substrate is referred to as a master mold from which a series of impressions, i.e. replicas, may be formed. In some instances, the master is useful as a retroreflective article, however replicas, including multi-generational replicas, are more commonly used as the retroreflective article. Direct machining is an excellent method for manufacturing master molds for small micro-cube arrays. Small microcube arrays are particularly beneficial for producing thin replica arrays with improved flexibility, such as continuous rolled goods for sheeting purposes. Micro-cube arrays are also more conducive to continuous process manufacturing. The process of manufacturing large arrays is also relatively easier using direct machining methods rather than other techniques. One example of direct machining is shown in U.S. Pat. No. 4,588,258 (Hoopman).
The invention, in one broad aspect, comprises forming geometric structures in a substrate by processing a first substrate having a first plurality of grooves therein. A replica of the first substrate is made in a second substrate. Then, a second plurality of grooves are formed in the second substrate. The replication process can comprise one or more individual replication procedures, and the second substrate can comprise a positive or negative copy of the first substrate. Geometric structures in the final substrate are formed in part by replication of the first plurality of grooves and in part by the formation of the second plurality of grooves.
The invention relates generally to a method of manufacturing a cube corner article comprising the steps of providing an initial non-unitary cube corner element array comprising a plurality of geometric structures including cube corner elements, producing a replica of the cube corner element array as a substrate suitable for forming retroreflective surfaces, and then removing part of the substrate material comprising the replica to form at least one cavity bounded by side walls in the replica at a depth at least that of the cube corner elements. The replica is then replicated to produce an additional directly machinable substrate suitable for forming retroreflective surfaces, the substrate comprising at least one raised section having side walls at a height at least that of the cube corner elements. Then at least one raised section is directly machined to form a raised zone comprising a plurality of geometric structures including cube corner elements bounded by at least two sets of parallel grooves.
The invention comprises a method of manufacturing a cube corner article comprising the steps of providing an initial directly machinable substrate formed as an initial non-unitary cube corner element array comprising a plurality of geometric structures including cube corner elements, and removing part of the substrate material comprising the array to form at least one cavity bounded by side walls in the substrate at a depth at least equal to the height of the cube corner elements. The initial substrate is then replicated to produce an additional directly machinable substrate suitable for forming retroreflective surfaces, with the additional directly machinable substrate comprising at least one raised section having side walls at a height at least that of the cube corner elements. At least one raised section is then directly machined to form a zone comprising a plurality of geometric structures including cube corner elements bounded by at least two sets of parallel grooves.
The invention relates generally to a cube corner article which is a machined replica of a non-unitary initial array comprising geometric structures including cube corner elements. The article has at least one directly machined raised zone of geometric structures including cube corner elements.